1. Field of the Invention
The present invention relates to an anti-reflective coating composition used in a photolithography process, which is one fabrication process for a semiconductor device, and a method for forming the pattern of a semiconductor device using the anti-reflective coating composition. More specifically, the present invention relates to a top anti-reflective coating composition usable in immersion lithography for the fabrication of a sub-50 nm semiconductor device, and a method for forming a pattern of a semiconductor device using the top anti-reflective coating composition.
2. Description of the Related Art
Photolithography is a process for the transfer of a semiconductor circuit pattern formed on a photomask to a wafer, and is one of the most important processes in determining the fineness and integration density of circuits in the fabrication of semiconductor devices.
In recent years, as the integration density of semiconductor devices has increased, new techniques have been developed that have been adapted to fine processing required in the fabrication of semiconductor devices. Under these circumstances, there is an increasing need for a fine processing technique in a photolithography process. That is, as the circuit line widths become finer and finer, the use of short-wavelength light sources for illumination, such as KrF, ArF, F2 and EUV excimer lasers, and high numerical aperture lenses is required. EUV, F2, ArF and KrF lasers in that order are preferred as light sources because of their short wavelengths.
Particularly, a number of studies on the development of sub-50 nm devices have been actively undertaken. In response to these studies, recent attention has been directed toward the development of suitable processing equipment and materials associated with the use of F2 and EUV as exposure light sources. Technical solutions for the use of F2 are satisfactory to some extent, but there are the following problems: 1) high-quality CaF2 is difficult to produce on an industrial scale within a short time, 2) since soft pellicles are likely to be deformed upon exposure to light at 157 nm, their life is short, and 3) hard pellicles incur considerable production costs, and are difficult to produce on a commercial scale due to the nature of light refraction.
On the other hand, since suitable light sources, exposure equipment, and masks are required to use EUV lasers, they are not yet suitable for practical use. Accordingly, the formation of finer high-precision photoresist patterns using a photoresist, and adapted for the use of an ArF excimer laser has now become a key technical task. Under these circumstances, immersion lithography has recently drawn attention.
Dry lithography is a current lithography process, and is an exposure system wherein air is filled between an exposure lens and a wafer. In contrast to dry lithography, immersion lithography, which corresponds to an NA scaling technique, is an exposure system wherein water is filled between an exposure lens and a wafer. Since water (with a refractive index (n)=1.4) is used as a medium for a light source in the immersion lithography, the NA is 1.4 times larger than that in the dry lithography using air (refractive index (n)=1.0). Accordingly, immersion lithography is advantageous in terms of its high resolution.
A problem encountered with the fabrication of a sub-50 nm semiconductor device is that alteration in the critical dimension (CD) of a photoresist pattern inevitably takes place, during a process for the formation of an ultra fine pattern, by standing waves, reflective notching, and diffracted and reflected light from an underlying layer due to the optical properties of the underlying layer on an overlying photoresist and due to variation in the thickness of the photoresist. To prevent the reflected light from reaching the underlying layer, a light-absorbing material, called an “anti-reflective coating”, at a wavelength band of light used as an exposure light source is introduced between the underlying layer and the photoresist. A bottom anti-reflective coating interposed between the underlying layer and the photoresist has been used to date. With the recent increase in the fineness of photoresist patterns, a top anti-reflective coating (TARC) has also been introduced in order to prevent the photoresist pattern from being disrupted by the reflected and diffracted light. Specifically, as the miniaturization of semiconductor devices makes photoresist patterns extremely fine, the use of a bottom anti-reflective coating alone cannot completely prevent the patterns from being disrupted by scattered reflection. Accordingly, a top anti-reflective coating is introduced to prevent the disruption of the patterns.
However, since conventional top anti-reflective coatings for use in dry lithography are water-soluble (in the case of using KrF or ArF laser), they cannot be applied to immersion lithography. In other words, since water is used as a medium for the light source in immersion lithography, it easily dissolves the conventional top anti-reflective coatings.
Accordingly, an ideal top anti-reflective coating for use in immersion lithography must satisfy the following requirements: 1) the top anti-reflective coating must be transparent to a light source; 2) the top anti-reflective coating must have a refractive index between 1.5 and 1.65, depending on the kind of underlying photosensitive film (i.e. photoresist) to be used; 3) when the top anti-reflective coating composition is coated on an underlying photosensitive film, it must not dissolve the photosensitive film; 4) the top anti-reflective coating must not be soluble in water upon light exposure; 5) the top anti-reflective coating must be soluble in a developing solution; and 6) the top anti-reflective coating must enable the formation of a vertical pattern.
The above-mentioned stringent requirements make the development of a suitable top anti-reflective coating for use in immersion lithography difficult. Particularly, a new concept top anti-reflective coating composition is needed to satisfy the requirement of 6).
Thus, there exists a strong need for the development of a top anti-reflective coating for use in immersion lithography which is water-insoluble and enables the formation of a vertical pattern upon formation of a semiconductor pattern.